Nikon has not announced a D4x, which is odd. Traditionally, the top of the line camera came first or at least in a group of announcements, followed by a mid-range camera with a lower resolution sensor (e.g. D3x along with D700 and D3s).
This go-round, we revel in the D800 at a mid-level price with the best imaging performance of the line, trailed by the D4 and the aging D700.
Why might this be?
Some will say that the D3x and D4 serve the market just fine so that is the reason— no need— but then one must wonder why the D4 was needed over the D3s.
The optimists (I count myself among them) will speculate on something much more interesting: ~60 megapixels would be magic as far as image quality were one to allow for downsampling, as I discussed a few days ago.
My prediction is that within a few years, high megapixel counts will be the norm (for image quality), though perhaps a “true color” non-Bayer sensor might emerge as an alternative. Those megapixels will likely be used to offer superior image quality, not necessarily more resolution, though one does not preclude the other.
Consider the Nikon D3200: assuming it has some of the secret sauce found in the Nikon D800 sensor, it will be a screaming deal (crummy body, but light weight and small). Since I expect one for review shortly, I will be answering that question. Worth noting is that the photosite density of the D3200 is diffraction limited by about f/4, which makes the f/3.5 - f/5.6 kit zoom a dubious pairing, but presumably it is such a dog that f/8 might be required for a decent image anyway.
Now consider the megapixels if the D3200 photosite size were scaled up to a full-frame ~58 megapixels, e.g., a 58-megapixel Nikon D4x. Which could offer a 29-megapixel downsampled file size with stunning per-pixel quality.
Why not? Strategically, a move like that would put even more pressure on Canon, making even diehard Canon holdouts ready to head to Ebay. It’s what I would do.
Of course, we might see a traditional move, wrapping a D4x big black body around the D800 sensor. That would be a good thing, but would give little impetus to the dynamics already set in motion by the D800.